Clinical and Molecular Studies in Families with Glaucoma and Related Diseases This study will document the clinical and genetic features of glaucoma and related diseases, including normal tension glaucoma (NTG). Researchers would like to define genetic influences and eventually isolate the genes causing those diseases. Glaucoma is an important cause of vision loss in the United States and worldwide. The disease is marked by a wearing down of the retina and optic nerve, often associated with increased pressure in the eye. It is often an inherited trait. This study will involve between 250 and 2,000 patients over a 5-year period. It will examine the natural history of the genotype, or genetic makeup, of a person and the phenotype, that is, visible situations produced by the interaction of the genotype and one's environment.